This invention relates to arrangements for preventing load change shocks in an internal combustion engine and, more particularly, to a new and improved arrangement for preventing such load shock.
In automobiles equipped with internal combustion engines, a so-called load change shock will occur on transition from engine braking operation to driving operation. Such shock may lead to longitudinal oscillations of the vehicle called jerking, especially at low engine speeds. This phenomenon is essentially caused by the kinetic energy of the combustion engine and the drive train which is released during a change in the direction of the load applied to the drive train because of elasticities and plays in the drive train and is partly transmitted to the body of the vehicle. Jerking resulting from such load changes can therefore be largely prevented if the kinetic energy built up during the load change is reduced to a minimum. This object is achieved by the arrangements described in the co-pending Muller Application Ser. No. 123,962, filed Nov. 23, 1987 and assigned to the same assignee as the present application, and in the published European Application No. 0 155 993. In the arrangements disclosed in those applications, the control commands to the power control element, e.g., a throttle valve or a control rod of an injection device, resulting from accelerator pedal actuation are transmitted with delay, i.e., with flattening and consequent prolongation of the increase in the level of the control signal.
Such delay in the transmission of an accelerator pedal command is undesirable, at least during normal operation of the combustion engine. However, in accordance with the present state of the art, such delays are accepted within a relatively large control range so that even more unacceptable instabilities of vehicle dynamics can be avoided or be reduced to an acceptable level.
In order to reduce undesirable load change phenomena to an acceptable level, the arrangement described by the abovementioned co-pending application provides a delay in accelerator pedal command transmission which is limited to a very small time range of the torque characteristic of the internal combustion engine, i.e., in the immediate vicinity of the passage of the torque characteristic through zero. This procedure relies on the fact that it is essentially only the sign reversal of the torque on transition from engine braking to driving which is responsible for the load change shock.
Whereas thus the co-pending application identified above produces a desired result by acting on the transmission of the acceleration command issued by the accelerator pedal, the arrangement according to the unpublished German Patent Application No. P 37 16 042.7 eliminates such a delayed transmission of a command signal. According to this application, rapid accelerator pedal movements cause a suppression of injection pulses to the injection pump in such a manner that initially a large number of injection pulses are suppressed whereas, during subsequent operation of the engine, the number of suppressed injection pulses is continuously reduced until finally all injection pulses are again provided. According to that patent application, an idle shut-off valve which is present in the system can be used for suppression of the pulses.
Thus, in accordance with the latter arrangement, injection pulses are completely suppressed and, as a result, a series of cylinder disconnections occurs. Contrary to the arrangement described in the co-pending Muller patent application, the last-mentioned German patent application does not provide for any limitation of the pulse control suppression to the region of the zero passage of the torque curve.